The present invention relates generally to processes for controlling environmental pollution, and more specifically, to chemical means for decontaminating substrates polluted with toxic substances.
The great difficulty in controlling toxic environmental pollutants is implied in the sheer tonnage of the chemical industries production. Whereas 25 million gallons of benzene solvent were manufactured in 1940, by the 1980's, this figure exceeded 2 billion gallons per year in the United States alone. In the last twenty years the production of general organic solvents rose more than 900%, while during the same period the production of plastics increased by more than 2000%, and synthetic fibers, for example, more than doubled that figure.
Unfortunately, however, the technology for handling and disposing of toxic waste and chemical by-products has not kept pace with the enormous growth of industry and its requirements for chemicals. In response to this problem, a new industry, the hazardous waste disposal industry, developed. The new industry promised to neutralize or recycle wastes, but no innovative technology to meet the growing problem economically developed. As a result, waste handlers have been forced to resort to land disposal, which is a storage technology and not a disposal technology, and only postpones the problem of ultimate disposal. In some instances, the toxic chemicals have been carelessly discharged into the environment, e.g. onto grounds or into landfills having inappropriate subsoils, and the like. For example, waste oils contaminated with dioxin, transformer oils containing polychlorinated biphenyls (PCBs), and a wide variety of waste solvents have been discharged, causing contamination of water supplies and creating other potential health risks.
Attempts to respond to leaking tank cars, spills and other environmental events and to decontaminate polluted grounds and other surfaces exposed to toxic substances frequently are met with delays and/or inadequate corrective measures. Often, time is of the essence to minimize environmental impact. Yet, cleanup can mean a relatively slow and costly process, e.g. removing the polluted substrates, such as by reclamation where, for instance, contaminated earth is excavated and transferred to a different location. Other methods of treating environmental events have been classified as being either unreliable or not adequately spontaneous as to be amenable to on-site treatment of the exposed substrate. For example, U.S. Pat. No. 4,430,208 (Pytlewski et al) describes methods used by analytical laboratories for decomposing PCBs with sodium metal in liquid ammonia i.e. solvated electrons. The patentees describe various drawbacks associated with this method, namely difficulty in preparing, cost of shipping and lack of stability in storage. Other shortcomings mentioned include sensitivities to oxygen and to water which impede reliable use of solvated electrons under field conditions.
Pytlewski et al then disclose a process for treatment of dielectric fluids contaminated with PCBs which obviates the foregoing problems with solutions of sodium in liquid ammonia. Instead of solvated electrons, their process provides for the use of NaPEG for decomposing PCBs. However, before contaminated dielectric fluids, for example, can be treated they are first subjected to a multistage extraction process, initially with PEG and then with cyclohexane to separate the organic e.g. PCBs for subsequent decomposition with NaPEG.
Accordingly, one aspect of the present invention includes the discovery that solvated electrons prepared from solutions of sodium metal in liquid ammonia are especially effective in the treatment of various contaminated substrates including organic solvents, dielectric fluids, and the like, polluted with halogenated organics e.g. PCBs, without the need for prior separation of the pollutant from the substrate. The present invention allows the contaminated substrate to be spontaneously treated without costly separation procedures.
Numerous agricultural chemicals have been recently found to be potentially toxic or environmentally harmful. Agents such as pesticides, herbicides, fungicides and fertilizers which are applied to large areas of ground in tonnage quantities are now being examined and in some cases banned for future use because of their toxicity. Materials such as DDT, EDB, chlordane and chlordecone are now severely restricted. In high concentrations these materials pose a serious health threat as they leach into the aquifers. Inexpensive, efficacious means for removing these materials from the soil or destroying them in-situ do not presently exist.
Kennedy, M. V. et al, Jour. Environ, Quality, Vol. 1, no. 1, 63-65, 1972, disclose laboratory studies relating to the treatment of herbicides, insecticides, fungicides and nematocides with liquid ammonia and metallic sodium or lithium conducted under controlled laboratory conditions. While the laboratory results were generally favorable, the experimental studies of Kennedy et al were conducted with essentially pure analytical grade materials. That is, Kennedy et al did not conduct their studies under field conditions where chemicals have actually diffused into the ground where they have become dispersed with the organic and inorganic components of earth, or where the pollutants have undergone partial decomposition, or in the presence of water which may be also be present. In the treatment of such naturally occurring substrates one would expect competing reactions to occur with the solvated electrons so as to interfere with the selectivity of the solvated electrons modifying the pesticide to a substance of lesser toxicity. Water, oxygen, nitrogen; metals like iron, copper, nickel, manganese, cobalt, etc., all naturally occurring in soils and the environment readily react with and/or impede the stability of solvated electrons. The mere fact that ammonia solution boils at -33.degree. C., by itself, has also deterred serious consideration t the practical application of solvated electrons as a viable means for treatment of soil and other porous substrates contaminated with such organics. Hence, alternative technologies have developed. For example, U.S. Pat. No. 4,632,742 (Tundo) discloses soils and other porous surfaces, like cement and sandstone, as well as smooth surfaces like glass contaminated with polyhalogenated organics, like PCBs treated with decontaminating reaction mixtures of alkali, polyethylene glycol and a source of free radicals. In treating contaminated soils and other porous and nonporous substrates methods of Tundo provide for removing moisture and enhancing decontamination by heating the soil or other porous substrate by irradiating with microwaves or by implanting electrodes in the soil for dehumidification. While the processes of Tundo may result in the destruction of the pollutant the need for dehumidification detracts from spontaneity and practicality of the process particularly when large clean-up areas are involved. Surface water will usually evaporate, but subterranean moisture can remain in the soil indefinitely.
Thus, contrary to what had been previously regarded as generally unworkable the present invention also includes the surprising discovery that contaminated substrates including porous, high surface area, as well as low surface area essentially smooth, nonporous surfaces having relatively high moisture levels, and even in the case of water saturated porous substrates like earth, soil, clay, sand, stone and heterogeneous mixtures of the same having essentially mud-like consistencies can be effectively decontaminated with solvated electrons. Methods of the present invention are effective notwithstanding competing reactions prompted by the presence of oxygen, iron, copper, etc. This was indeed surprising in view of the substantial technical authority viewing water, for example, and various metals as antagonists of solvated electrons. Accordingly, because the process was found to be also operative in the presence of moisture/water, pretreatment steps normally employed for evaporation of moisture can be eliminated. This provides for a more spontaneous method of treatment at the situs of the event which reduces the potential for damage to the environment. An extension of this aspect of the invention includes treatment processes in which solvated electrons are used in the reclamation of bulk quantities of chemically contaminated soils and other porous, high surface area substrates like brick and concrete with materials which are economical and environmentally benign.
It has been pointed out, according to the present invention, naturally occurring porous surfaces like soils, clays, sand, stone, wood, etc., as well as man-made materials like concrete, asphalt (roadways), brick, including plastics, metallic substrates, etc., may become contaminated with organic compounds and other hazardous substances requiring prompt remedial in-situ or "batch" treatment. The latter method generally includes excavation and removal of contaminated soils, or recovery of articles of manufacture, such as hardware, tools and equipment like transformers and their cores, etc., which can be transferred to a reactor or other containment vessel and decontaminated by flushing with solutions of solvated electrons. The decontaminated soils, articles, materials and equipment, i.e. substrates, can thereby be reclaimed.
The expression--contaminated or polluted substrate--is intended generally to include any solid, liquid or gaseous naturally occurring or manufactured material, substance or article having a pollutant which may be entrained in, dissoved in, molecularly bonded or physically sorbed, i.e. adsorbed or absorbed thereto, rendering it potentially unsafe to a biological system. It has been observed, particularly in the case of porous substrates like concrete, asphalt, soils and clays, that contaminants can become sorbed or bonded to the substrate making decontamination and reclamation slow and inefficient. Accordingly, as a further aspect of the invention it was found that substrates having contaminates sorbed or bonded thereto can be effectively treated with the reactant, ammonia, which is also used in solvating electrons for reduction and destruction of the contaminant. It was discovered that ammonia applied to or mixed with the substrate prior to destruction of the contaminant effectively desorbs or releases the pollutant, increasing the efficiency of solvated electrons in the decontamination process. Thus, the present invention embraces the discovery that ammonia and anhydrous liquid ammonia may be used in desorption and solvation of electrons respectively in the decontamination of substrates.
As previously indicated, problems associated with pollution control frequently involve treatment of a substrate which has become contaminated with a toxic substance. The substrate may be treated in-situ or removed and processed in a batch type method with solvated electrons in one or more process steps including, for instance, pretreatment with a heat generating desorbent e.g. ammonia. Such methods degrade the toxic substance and achieve reclamation of the substrate, e.g. soil. Frequently, however, in the chemical industry there are large volumes of toxic, potentially hazardous, unwanted, discontinued or off-spec materials which cannot be safely disposed of without harm to the environment. For example, there is evidence that chlorofluorocarbons (CFCs) like certain Freons.RTM., Halons.RTM., etc., used as refrigerants and propellants in aerosol containers are potentially harmful to the outer ozone layer which shields the earth from harmful UV light. Alternative frigerants and propellants are being developed while certain CFCs are being phased out. However, there are still sizeable reserves of chlorofluorocarbons on hand which must be treated and converted to environmentally benign substances. Accordingly, the present invention contemplates not only methods for the decontamination of polluted substrates, but also chemically degrading bulk volumes of unwanted potentially harmful substances like CFCs by dehalogenation. More specifically, in the case of CFCs, the invention contemplates treatment with solvated electrons for selective removal of at least one chlorine atom without defluorination to form modified CFCs of lesser toxicity which are environmentally benign and which still possess the desired utilities of CFCs. In other words, this aspect of the invention includes methods for converting hazardous substances to materials of reduced toxicity and impact on the environment or to materials which can be recovered as useful by-products.